Aux-lane suppression + PA geometry fixes; probe/verify tooling

MapBuilder.luau
  - Suppress the aux lane across samples 525-550 (AUX_SUPPRESS_FROM/TO),
    honoring the user's hand deletion in Studio so a rebuild no longer
    regenerates it.
  - Smoothstep the width ramp over AUX_BLEND=5 samples on each side. A hard
    cut produced a 26-stud lateral fence jog; the blend removes it.
  - DO NOT remove this suppression. Re-enabling it resurrects geometry the
    user deleted by hand.

rokit.toml
  - rojo 7.5.1 -> 7.7.0 to match the auto-updating Studio plugin.
    Server older than plugin fails the handshake with
    "attempt to index number with 'protocolVersion'".

tools/
  - 34 read-only probe/verify/capture scripts used to measure the datamodel
    instead of reasoning from source.

Verified-good baseline at this commit:
  total parts       16788
  PAWestSlip        60 segs, 34.4 deg total bend, worst 1.4, 0 kinks >5
  PAEastSlip        60 segs, 30.7 deg total bend, worst 1.3, 0 kinks >5
  AuxLane parts     30 (samples 525-550 deliberately absent)
  barrier coverage  823 samples, 0 unguarded
  fence jogs >10st  0

tools/probe_slip_envelope.luau

@@ -0,0 +1,109 @@
+-- Measure the envelope a SIMPLE straight slip-ramp must live in.
+-- User's drawing: short stubs peeling off the mainline at a shallow angle,
+-- running roughly PARALLEL to the highway in the strip between the mainline
+-- edge and the PA lot's north edge, descending an S onto the apron.
+--
+-- We need to know, in real numbers:
+--   1. Where the mainline actually runs across the PA frontage (samples,
+--      heading, deck Y) -- is it straight enough for a parallel slip?
+--   2. Where the lot's north edge is, and how wide the clear strip is
+--      between the mainline's south edge and that lot edge.
+--   3. Deck Y vs apron Y (the height the S-curve must lose).
+--   4. What is already sitting in that strip that a ramp would hit.
+
+local RS = game:GetService("ReplicatedStorage")
+local HttpService = game:GetService("HttpService")
+local Circuit = require(RS:WaitForChild("Shared"):WaitForChild("Circuit"))
+
+local samples = Circuit.samples
+local n = #samples
+local c = Circuit.PA_CENTER
+
+-- Nearest mainline sample to the PA centre.
+local bestIdx, bestD = 1, math.huge
+for i = 1, n do
+    local p = samples[i].pos
+    local d = (Vector3.new(p.X, 0, p.Z) - Vector3.new(c.X, 0, c.Z)).Magnitude
+    if d < bestD then bestD, bestIdx = d, i end
+end
+
+-- Walk a band around the PA frontage and report heading + deck Y, so we can
+-- see how straight the mainline is and where a parallel slip could sit.
+local band = {}
+for k = -40, 40, 5 do
+    local i = ((bestIdx - 1 + k) % n) + 1
+    local s = samples[i].pos
+    local nx = samples[(i % n) + 1].pos
+    local hdg = math.deg(math.atan2(nx.Z - s.Z, nx.X - s.X))
+    local d = (Vector3.new(s.X, 0, s.Z) - Vector3.new(c.X, 0, c.Z)).Magnitude
+    table.insert(band, {
+        k = k, idx = i,
+        x = math.floor(s.X), y = math.floor(s.Y + 0.5), z = math.floor(s.Z),
+        hdg = math.floor(hdg + 0.5),
+        distPA = math.floor(d),
+    })
+end
+
+-- The apron / lot floor: bounds and surface height.
+local map = workspace:FindFirstChild("Map")
+local floor = map and map:FindFirstChild("PAFloor", true)
+local lot = nil
+if floor then
+    lot = {
+        name = floor.Name,
+        surfaceY = floor.Position.Y + floor.Size.Y / 2,
+        x_min = math.floor(floor.Position.X - floor.Size.X / 2),
+        x_max = math.floor(floor.Position.X + floor.Size.X / 2),
+        z_min = math.floor(floor.Position.Z - floor.Size.Z / 2),
+        z_max = math.floor(floor.Position.Z + floor.Size.Z / 2),
+    }
+end
+
+-- What already occupies the strip between the mainline and the lot's north
+-- edge? Anything here is a collision candidate for a parallel slip ramp.
+-- Strip = north third of the lot bbox, i.e. Z above (z_max - 220).
+local obstacles = {}
+if lot then
+    local stripZ = lot.z_max - 220
+    for _, d in ipairs(workspace:GetDescendants()) do
+        if d:IsA("BasePart") then
+            local p = d.Position
+            if p.Z >= stripZ and p.Z <= lot.z_max + 160
+               and p.X >= lot.x_min - 60 and p.X <= lot.x_max + 60 then
+                local key = d.Name
+                local e = obstacles[key]
+                if not e then
+                    e = { n = 0, x_min = 1e9, x_max = -1e9, z_min = 1e9,
+                          z_max = -1e9, y_max = -1e9 }
+                    obstacles[key] = e
+                end
+                e.n += 1
+                e.x_min = math.min(e.x_min, p.X); e.x_max = math.max(e.x_max, p.X)
+                e.z_min = math.min(e.z_min, p.Z); e.z_max = math.max(e.z_max, p.Z)
+                e.y_max = math.max(e.y_max, p.Y + d.Size.Y / 2)
+            end
+        end
+    end
+end
+
+local obsOut = {}
+for k, e in pairs(obstacles) do
+    table.insert(obsOut, {
+        name = k, n = e.n,
+        x = math.floor(e.x_min) .. ".." .. math.floor(e.x_max),
+        z = math.floor(e.z_min) .. ".." .. math.floor(e.z_max),
+        ytop = math.floor(e.y_max),
+    })
+end
+table.sort(obsOut, function(a, b) return a.n > b.n end)
+while #obsOut > 25 do table.remove(obsOut) end
+
+return HttpService:JSONEncode({
+    bestIdx = bestIdx,
+    nearestDist = math.floor(bestD),
+    pa_center = { math.floor(c.X), math.floor(c.Y), math.floor(c.Z) },
+    pa_radius = Circuit.PA_RADIUS,
+    band = band,
+    lot = lot,
+    strip_obstacles = obsOut,
+})